1. Field of the Invention
The present invention relates to a light beam scanning apparatus and, more particularly, to a light beam scanning apparatus for sweeping a light beam to read out or record image information.
2. Description of the Prior Art
In the conventional light beam scanner, a light beam emitted from a light source such as a laser is reflected and swept by a mirror which is rotated by a galvanometer. Where such a device is applied to an image information recording system, the light beam is modulated in response to an image information signal using, for example, an acoustooptical modulator (AOM), and a photosensitive recording medium is scanned with the modulated beam to record the image information thereon. On the other hand, where the scanner is applied to an image information read-out or reproducing system, a medium carrying an image is scanned with the light beam and the light having passed through or reflected by the medium is detected to read out the information. Particularly, when a radiation image stored in a stimulable phosphor sheet is read out, the laser beam is used as stimulating rays, and the read out of the radiation image is performed by scanning the sheet with the laser beam and photoelectrically detecting the light emitted from the sheet to obtain signals corresponding to the radiation image.
Whether the light beam scanner of the type as described above is applied to an image information recording system or to an image information read out system, it is desirable that the light beam is swept at a constant speed.
In an image information recording system, for example, an image with a uniform quality can be recorded if exposure time per pixel is constant. In an image information read out system, on the other hand, an image can uniformly be reproduced if the integration time per pixel is constant.
However, such a scanner has the defect that it includes one or more mirrors, a galvanometer and other mechanically movable elements in its optics which cannot readily be brought to or held in optimal conditions by manual adjustment. For example, even a very small misalignment of a mirror greatly effects an offset of the light beam in the initial position. In addition, the influence of the fluctuation of ambient temperature on its optics is not negligible.
To set up a constant scanning speed and obtain an image of high quality, therefore, a system is desirable which requires minimum manual adjustment, and in which initial position offset of light beam, and the like can be automatically adjusted.